The invention relates generally to systems and methods of subnetwork connection protection. More specifically, certain embodiments generally relate to protection switching mechanisms and methods that afford multiple layers of protection through combined inter-leg and intra-leg switching.
A wide variety of communications networks exist today and are continuously being improved. These communications networks support large volumes of traffic and offer a wide variety of services. There is increased need for the reliable and continuous operation of such networks due to the ever increasing traffic loads and growing reliance on communications networks for both business and personal use. An important element of reliability is the ability to quickly detect failures within the network and to automatically correct or restore the communications link. Self-healing methods, which automatically restore network connections after failure, exist for certain network architectures. Self-healing methods typically rely on distributed control to ensure fast fault recovery and to protect against catastrophic failure.
In certain network architectures, protection from failure has been addressed by adding redundant hardware and traffic channels. Typically, redundant networks include backup boards or cards that convey traffic signals identical to the traffic signals on a primary board or card. The primary and back-up cards are also referred to as working and protection cards. Throughout, the terms “primary” and “working” are used interchangeably, and the terms “back-up” and “protection” are used interchangeably. When a failure occurs on the primary board, the traffic to the backup board is utilized to ensure reliable and continuous service.
One example of a redundant protection scheme is a “1+1 protection scheme” in which every primary board is uniquely associated with a backup board. The 1+1 protection scheme protects against single board failures by affording hitless protection switching, namely the ability to switch in a backup board in the event the primary board fails before frame synchronization is lost.
Another conventional protection scheme is sub-network connection protection (SNCP). SNCP is a SDH-standard path protection mechanism (defined in ITU-T G.841) similar to UPSR (Bellcore GR-1400) in the SONET standard. In accordance with SNCP, a permanent source bridge is provided on the transmit side, and a selector function is implemented on the receive side. SNCPs are unidirectional, and switching is performed in a manner very similar to 1+1 and UPSR protection schemes. The ITU-T G.841 and Bellcore GR-1400 standards are incorporated herein in their entirety by reference.
Another conventional protection scheme is “1:N protection”, which allows a single backup or protection card to provide shared or limited protection to multiple primary or working cards. In a 1:N protection scheme, multiple working cards convey unique and separate traffic signals, but are protected by a common, single protection card. The working cards are afforded a priority distribution that determines the extent to which each working card is protected by the protection card.
However, conventional protection schemes have experienced limited success. Conventional protection schemes, such as the 1+1, SNC (UPSR) and 1:N protection schemes, correlate each working port, path or card respectively with at most a single protection port, path or card. In the 1:N protection scheme, multiple working cards are correlated to a common single protection card. While these protection schemes are able to adequately address failures within one or a limited number of working cards, these protection schemes do not afford added backup in the event that the first layer of protection experiences failures or faults. For example, in the 1+1 protection scheme, when the working card and the protection card both fail, a catastrophic failure would then be experienced and frame synchronization would be lost. In SNC and UPSR protection schemes, when both work and protect paths fail the traffic would be lost. In the 1:N protection scheme, a single protection card supports multiple working cards. Hence, once a working card fail and fully load the protection card, the remaining working cards have no further backup protection. Also, once the protection card in the 1:N protection scheme fails, no additional layers of protection are afforded.
A need remains for an improved protection scheme for paths or sub-network connections.